The launch, set to take place between Thursday and next Monday, has prompted neighbours such as the Philippines to re-route their air traffic just in case. Regional powers also worry it could be the prelude to another nuclear test, a pattern the hermit state set in 2009.

Japan said it would shoot down the rocket if it crossed its airspace.

The launch of the Unha-3 rocket, which North Korea says will merely put a weather satellite into space, breaches U.N. sanctions imposed to prevent Pyongyang from developing a missile that could carry a nuclear warhead.

It coincides with the 100th birthday celebrations of the founder of North Korea, Kim Il-sung, whose grandson, Kim Jong-un, now rules. Kim Il-sung died in 1994.